Light-emitting device

ABSTRACT

A light-emitting device comprises a light-emitting stack comprising a first surface and a second surface opposite to the first surface; a first electrode formed on the second surface of the light-emitting stack; a current blocking layer formed on the first surface of the light-emitting stack and corresponding to a location of the first electrode; and a second electrode covering the current blocking layer and comprising a plurality of first metal layers and a plurality of second metal layers alternating with the plurality of first metal layers, wherein the plurality of first metal layers is discontinuous.

REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication, Ser. No. 14/681,291, which claims the right of prioritybased on TW application Serial No. 103112952, filed on Apr. 8, 2014, andthe contents of which are hereby incorporated by references in theirentireties.

TECHNICAL FIELD

The application relates to a light-emitting device, and moreparticularly, to a light-emitting device comprising a reflective layer.

DESCRIPTION OF BACKGROUND ART

The lighting theory of light-emitting diodes (LEDs) is that electronsand holes between an n-type semiconductor and a p-type semiconductor arecombined in the active layer to release light. Due to the difference oflighting theories between LEDs and incandescent lamps, the LED is called“cold light source”. An LED has the advantages of good environmenttolerance, a long service life, portability, and low power consumptionso it is regarded as another option for the lighting application. LEDsare widely adopted in different fields, for example, traffic lights,backlight modules, street lights, and medical devices and replaceconventional light sources gradually.

An LED has a light-emitting stack which is epitaxially grown on aconductive substrate or an insulative substrate. The so-called “verticalLED” has a conductive substrate and includes an electrode formed on thetop of a light emitting layer; the so-called “lateral LED” has aninsulative substrate and includes electrodes formed on two semiconductorlayers which have different polarities and exposed by an etchingprocess. The vertical LED has the advantages of small light-shading areafor electrodes, good heat dissipating efficiency, and no additionaletching epitaxial process, but has a problem that the conductivesubstrate served as an epitaxial substrate absorbs light easily and isadverse to the light efficiency of the LED. The lateral LED has theadvantage of radiating light in all directions due to a transparentsubstrate used as the insulative substrate, but has disadvantages ofpoor heat dissipation, larger light-shading area for electrodes, andsmaller light-emitting area caused because of the epitaxial etchingprocess.

The abovementioned LED can further connect to/with other components forforming a light-emitting device. For a light-emitting device, the LEDcan connect to a sub-carrier by the substrate side or by solderingmaterial/adhesive material between the sub-carrier and the LED. Besides,the sub-carrier can further comprise a circuit electrically connected toelectrodes of the LED via a conductive structure, for example, a metalwire.

SUMMARY OF THE APPLICATION

A light-emitting device comprises: a light-emitting stack including afirst surface and a second surface opposite to the first surface,wherein the light-emitting stack emits a light having a wavelengthbetween 365 nm and 550 nm; and a first electrode formed on the firstsurface and including a first metal layer and a second metal layeralternating with the first metal layer, wherein the first electrode hasa reflectivity larger than 95% for reflecting the light, and the secondmetal layer has a higher reflectivity relative to the light than that ofthe first metal layer.

A light-emitting device comprises: a light-emitting stack comprising afirst surface and a second surface opposite to the first surface,wherein the light-emitting stack emits a light having a wavelengthbetween 365 nm and 550 nm, and the first surface comprises a firstportion having a first conductivity and a second portion having a secondconductivity; a first electrode, comprising a first electrode pad and areflective stack comprising a first metal layer and a second metal layeralternating with the first metal layer, wherein the reflective stack iselectrically connect to the first portion of the first surface and has areflectivity larger than 95% for reflecting the light, and the secondmetal layer has a higher reflectivity relative to the light than that ofthe first metal layer; a second electrode, comprising a second electrodepad and an ohmic contact layer formed on the second portion of the firstsurface; and a carrier comprising a first contact pad electricallyconnected to the first electrode pad and a second contact padelectrically connected to the second electrode pad.

A light-emitting device comprises a light-emitting stack comprising afirst surface and a second surface opposite to the first surface; afirst electrode formed on the second surface of the light-emittingstack; a current blocking layer formed on the first surface of thelight-emitting stack and corresponding to a location of the firstelectrode; and a second electrode covering the current blocking layerand comprising a plurality of first metal layers and a plurality ofsecond metal layers alternating with the plurality of first metallayers, wherein the plurality of first metal layers is discontinuous.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E illustrate a manufacturing method of a light-emittingdevice in accordance with a first embodiment of the present application;

FIG. 1F illustrates a light-emitting stack in accordance with the firstembodiment of the present application;

FIG. 2 illustrates a light-emitting device in accordance with a secondembodiment of the present application.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1A to 1E, a manufacturing method of a light-emittingdevice in accordance with a first embodiment of the present applicationis disclosed.

As shown in FIG. 1A, a buffer layer 103 and a light-emitting stack areepitaxially grown on a growth substrate 101. The growth substrate 101can comprise transparent substrate such as sapphire, or conductivesubstrate such as SiC. The buffer layer 103 can comprise anun-intentionally doped AlN, AlGaN or GaN, and the light-emitting stack108 can comprise GaN. The buffer layer 103 can reduce the defectresulted from the lattice mismatch between the growth substrate 101 andthe light-emitting stack 108. The light-emitting stack 108 can comprisea first semiconductor layer 102, an active layer 104, and a secondsemiconductor layer 106. The first semiconductor layer 102 and thesecond semiconductor layer 106, for example, can be cladding layer orconfinement layer, capable for providing electrons and holes, and theelectrons and holes can be combined in the active layer 104 to emitlight. The first semiconductor layer 102, the active layer 104, and thesecond semiconductor layer 106 can comprise III-V group semiconductormaterial such as Al_(x)In_(y)Ga_((1-x-y))N, 0≦x, y≦1; (x+y)≦1. Inaccordance with the material of the active layer 104, the emitted lightthereof can be green light having a wavelength between 530 nm and 570nm, blue light having a wavelength between 450 nm and 490 nm, orultraviolet light having a wavelength between 365 nm and 405 nm. Thefirst semiconductor layer 102 can comprise an n-type semiconductor layerand the second semiconductor layer 106 can be a p-type semiconductorlayer.

As shown in FIG. 1B, a patterned current-blocking layer 110 is formed onthe first surface 108 a of the light-emitting stack 108, that is, thepatterned current-blocking layer 110 is formed on the secondsemiconductor layer 10. The current blocking layer can be insulatingoxide such as SiO₂ or TiO₂, or can be nitride such as SiN_(x).

As shown in FIG. 1C, a first electrode 112 can be formed on the firstsurface 108 a of the light-emitting stack 108 and cover the currentblocking layer 110. Then a barrier layer 114 comprising a first barrierlayer 114 a and a second barrier layer 114 b can be formed on theuncovered region of the first surface 108 a and the first electrode 112.The current blocking layer 110 is entirely covered by the firstelectrode 112, and on the first surface 108 a the first electrode 112 isnarrower than the barrier layer 114.

The first electrode 112 can be a reflective stack comprising a firstmetal layer 112 a and a second metal layer 112 b alternating with thefirst metal layer 112 a, and the thermal stability of the first metallayer 112 a is better than that of the second metal layer 112 b, and thereflectivity of the second metal layer 112 b is higher than that of thefirst metal layer 112 a. For example, the first metal layer 112 a can beAl and the second metal layer 112 b can be Ag. Further referring to FIG.1F, the first metal layer 112 a and a second metal layer 112 b canalternate with each other for 2 to 12 times. In the embodiment, thefirst electrode 112 comprises a first metal layer 112 a directlycontacting the first surface 108 a. The barrier layer 114 can comprisean alloy or a stack comprising Ti, W, Pt, and Ni. The thickness of thefirst metal layer 112 a can be between 1˜10 Å, and the thickness of thesecond metal layer 112 b can be between 100˜700 Å. To be more specific,the thickness of the first metal layer 112 a can be approximately 3 Å,wherein the first metal layer 112 may be discontinuous or embedded inthe second metal layer 112 b, and the total thickness of the firstelectrode 112 can be between 1400 Å and 1500 Å, or even thicker than1500 Å. To make the first electrode 112 ohmically contact the secondsemiconductor layer 106 of the light-emitting stack 108, a Rapid ThermalAnnealing (RTA) process can be proceeded under a condition of 500° C.and 40 minute after the first electrode 112 is formed. For example, whenthe second metal 112 b is Ag and the second semiconductor layer 106 isp-type GaN, a high temperature annealing for Ag and p-type GaN isproceeded, and the first metal layer 112 a can stabilize the secondmetal layer 112 b when the high temperature annealing is performed.Beside pure Al, the first metal layer 112 a can be an alloy or stackcomprising Al, Ti, W, Pt or Ni.

Referring to FIG. 1D, a conductive substrate 118 is provided to attachto the light-emitting stack 108 via a conductive bonding layer 116. Theconductive bonding layer 116 is between the conductive substrate 118 andthe barrier layer 114 and comprises metal such as Au, In, Ni or thealloy thereof. The light-emitting stack 108 comprises a firstsemiconductor layer 102, an active layer 104, and a second semiconductorlayer 106, and is between the growth substrate 101 and the conductivesubstrate 118. A laser (not shown) can be provided to decompose thebuffer layer 103 so as to remove the growth substrate 101, and residuesof the buffer layer 103 can be cleaned by dry etching and wet etching.

Please refer to FIG. 1E, the light-emitting stack 108 can expose asecond surface 108 b after the removal of the buffer layer in FIG. 1D.The second surface 108 b serves as a primary light-extraction surfaceand is also a surface of the first semiconductor layer 102, and thesecond surface 108 b can be a roughing surface to increaselight-extraction efficiency. A second electrode 120 can be formed on thesecond surface 108 b and corresponds to the location of the currentblocking layer 110.

When a driving current is injected into the light-emitting stack 108 viathe second electrode 120 and the conductive substrate 118, the activelayer 104 can emit light L resulted from the combination of electronsand holes, and the light L can be reflected by the first electrode 112and extracted out from the second surface 108 b. In the embodiment, whenthe wavelength of the light is between 365 nm to 550 nm, thereflectivity of the first electrode 112 can be higher than 95%, and canbe even up to 98% to 100%. In the embodiment, the first electrode 112 iscomposed of the first metal layer 112 a having high thermal stabilityand the second metal layer 112 b having high reflectivity so the problemof substantially reduced reflectivity caused by the high temperatureannealing of high reflective metal (e.g. Ag) and the semiconductor layerin the conventional art is relieved. The origin of the problem is thatthe high reflectivity metal such as Ag is unstable after hightemperature annealing. Moreover, when the light-emitting stack ofconventional art receives a high current larger than 350 mA, the highreflectivity metal becomes more unstable and the reflectivity thereof isfurther decreased. In the embodiment, the first metal layer 112 a has ahigh reflectivity close to that of the second metal 112 b and has abetter ohmic contact with the second semiconductor layer 106, and thefirst metal layer 112 a has better thermal stability than that of thesecond metal layer 112 b, therefore the first metal layer 112 a can keepthe second metal 112 b stable under high temperature annealing to avoidthe reflectivity from dramatically reducing after high temperatureannealing. Besides, in one experiment, the reflectivity of the firstelectrode 112 is not obviously decreased even a current higher than 350mA is provided to the light-emitting stack 108.

Referring to FIG. 2, a light-emitting device in accordance with a secondembodiment of the present application is illustrated. A light-emittingdevice 200 comprises: a light-emitting stack 210 comprising a firstsurface 210 a and a second surface 210 d opposite to the first surface210 a, and the light-emitting stack 210 emits a light L₁ havingwavelength equal to that of the light L of the first embodiment, and thefirst surface 210 a comprises a first portion 210 b having a firstconductivity and a second portion having a second conductivity, a firstelectrode 217 comprising a first electrode pad 226 and a reflectivestack comprising a first metal layer 214 a and a second metal layer 214b alternating with the first metal layer 214 a, wherein the reflectivestack is electrically connected to the first portion 210 b of the firstsurface 210 a and having a reflectivity lager than 95% relative to lightL₁ so the light L₁ is emitted out the light-emitting stack 210 from thesecond surface 210 d, a second electrode 250 comprising a secondelectrode pad 224 and an ohmic contact layer 231 formed on the secondportion 210 c of the first surface 210 a, and a carrier 218 comprising afirst conductive pad 222 electrically connected to the first electrode217 and a second conductive pad 220 electrically connected to the secondelectrode pad 224. The light-emitting stack 210 comprises a firstsemiconductor layer 204 having two sides on which the second portion 210c of the first surface 210 a and the second surface 210 d are formed on,respectively, an active layer 206, and a second semiconductor layer 208comprising the first portion 210 b of the first surface 210 a. Thesecond portion 210 c of the first surface 210 a is formed by removing apart of the second semiconductor layer 208 and the active layer 206. Aninsulating layer 203 is formed on the first surface 210 a of thelight-emitting stack 210 and a trench can be formed by etching process,and a metal can be filled into the trench to form a conductive channel.The first electrode 217 can further comprise a barrier layer 216covering the reflective stack formed by the first metal layer 214 a andthe second metal layer 214 b and a first conductive channel 228penetrating through the insulating layer 203 wherein the two ends of thefirst conductive channel 228 are electrically connected to the barrierlayer 216 and the first electrode pad 226. The first metal layer 214 aand the second metal layer 214 b comprise the same material as those inthe first embodiment. The first metal layer 214 a can directly contactthe second semiconductor layer 208, and in the embodiment the firstmetal layer 214 a and the second metal layer 214 b can alternate witheach other for 2 to 12 times, therefore further raising the reflectivityover 95% relative to the light L₁, even up to 98% to 100%. In anotherembodiment, a metal oxide (not shown) can be formed between the firstelectrode 217 and the second semiconductor layer 208 to promotecurrent-spreading effect. The second electrode 250 further comprises asecond conductive channel 230 having two ends connected to the ohmiccontact layer 231 and the second electrode pad 224. A transparentsubstrate 202 can be formed on the second surface 210 d of thelight-emitting stack 210, and the transparent substrate 202 can be agrowth substrate such as sapphire for epitaxially growing thelight-emitting stack 210. In another embodiment, the transparentsubstrate 202 can be removed and the second surface 210 d can be aroughing surface by an etching process. The first electrode pad 226, thesecond electrode pad 224, the first conductive channel 228 and thesecond conductive channel 230 can be a stack composed of metals such asNi, Au and/or Ti. The ohmic contact layer 231 of the first electrode 250can be a stack composed of metals such as Cr, Pt, and/or Au. Areas ofthe first electrode pad 226 and the second electrode pad 224 can belarger than the cross-sectional areas of first conductive channel 228and the second conductive channel 230, respectively, and both of thefirst electrode pad 226 and the second electrode pad 224 are extended onthe surface of the insulating layer 203 for receiving a high currentfrom the carrier 218.

Although the present application has been explained above, it is not thelimitation of the range, the sequence in practice, the material inpractice, or the method in practice. Any modification or decoration forpresent application is not detached from the spirit and the range ofsuch.

What is claimed is:
 1. A light-emitting device, comprising: alight-emitting stack comprising a first surface and a second surfaceopposite to the first surface; a first electrode formed on the secondsurface of the light-emitting stack; a current blocking layer formed onthe first surface of the light-emitting stack and corresponding to alocation of the first electrode; and a second electrode covering thecurrent blocking layer and comprising a plurality of first metal layersand a plurality of second metal layers alternating with the plurality offirst metal layers, wherein the plurality of first metal layers isdiscontinuous.
 2. The light-emitting device of claim 1, wherein theplurality of second metal layers alternates with the plurality of firstmetal layers for 2 to 12 times.
 3. The light-emitting device of claim 1,wherein the plurality of first metal layers comprises Al, Ti, W, Pt orNi.
 4. The light-emitting device of claim 1, wherein the plurality ofsecond metal layers comprises a thickness between 100 Å and 700 Å. 5.The light-emitting device of claim 1, wherein the light-emitting stackcomprises a first semiconductor layer comprising the second surface, asecond semiconductor layer comprising the first surface and an activelayer between the first semiconductor layer and the second semiconductorlayer, and the first electrode is formed on a part of the first surface,and the light is emitted out the light-emitting stack from the secondsurface.
 6. The light-emitting device of claim 1, wherein one of theplurality of first metal layers directly contacts the first surface ofthe light-emitting stack.
 7. The light-emitting device of claim 1,further comprising a conductive substrate, and a conductive bondinglayer formed between the conductive substrate and the second electrode.8. The light-emitting device of claim 1, wherein the first electrodecomprises a pattern.